Adjustable resistance device



July 11, 1933.: c. L. wElcHELT ADJUSTABLE RESISTANCE DEVICE I Filed NOV.l2, 1930 #VVE/V70? A Tok/vir Patented July 11, 1933 UNITED STATES PATENTOFFICE CARI. L. WEICHELT, OF PHILADELPHIA, PENNSYLVANIA, ASSIGNOR TOWIRT COMPANY, 0F PHILADELPHIA, PENNSYLVANIA, A CORPORATION 0F MAINEADJUSTABLE RESISTANCE DEV'ICE Application filed November 12, 1930.Serial No. 495,017.

My invention relates to adjustable resistance devices which may beutilized as potentiometers for varying simultaneously by adjustment thedifferences in potential, through two separate resistance elements ormembers, between two points associated respectively with the saidmembers. AThe device is of especial utility as a volume control meansfor radio reception apparatus.

The general object of the invention is to provide a resistance device ofthe character indicated having at least two resistance elements locatedin cooperative relation to movable contacts which contacts are mountedupon a single support and are movable simultaneously into differentpositions relatively to the said resistance elements or members.

To the foregoing and other ends the invention comprehends theconstruction and arrangement as hereinafter described in detail,particularly pointed out in the appended claims, and as shown in theaccompanying drawing wherein I have illustrated one embodiment of theinvention in a form at present preferred by me but it will be understoodthat the invention may be embodied in other forms of construction thanthat illustrated and that changes in the details of construction may bemade within the scope of the claims without departing from the saidinvention or the principle thereof.

In the drawing:

Fig. 1 is a view in elevation of one end of a device embodying theinvention, the top or cover of the casing thereof being removed;

F ig. 2 is aview in longitudinal central section taken on the line 2 2of Fig. 1, the top or cover being shown in place upon the open end ofthe casing of the device;

Fig. 3 is a transverse sectional view taken on the line 3 3 of Fig. 2;

Fig. 4 is a longitudinal sectional View of the casing and in crosssection of the resistance elements mounted therein;

Fig. 5 is a view inside elevation of a resistance element removed fromthe casing and in extended or straightened condition; and

Figs. 6, 7 and 8 are perspective views of certain elements embodied inthe construction.

ln the drawing l have shown at 1 a casing of cup shape consisting ofsuitable insulating material as, for example, a phenolic condensationproduct. The side of the casing Ais of stepped formation; that is tosay, the diameter in adjoining relation to the bottom thereof, as at 2,is less than the diameter of an upper intermediate portion as shown at3. rllhese differences in diameter provide a shoulder or ledge 4. rlheextreme outer end portion of the casing is of greater diameter than theintermediate portion, as is indicated at 5.

'l wo resistance elements or members 7 and 8 are employed in theconstruction, each of which comprises resistance wires 10 of requiredgauge and of suitable material wound around thin elongated strips 11 and12 of suitable insulating material as, for example, condensite or afabric saturated with a phenolic condensation product. The strip 11 isof somewhat shorter length than the strip 12 for a reason which willbecome apparent as this description proceeds.

The coils `of wire 10 at the opposite ends of the strips 11 and 12 areheld in place by overlying holding metal portions 13 which projectinwardly from metal clips 14 the opposite ends of which are bent aroundthe edges of the strips 11 and 12 and operate to hold the clips inplace. The opposite ends of the strips 11 and 12 are cut on the bias asshown in the drawing; that is, along lines inclined with respect to thelength of the said strips. These strips are bent into circular form andare inserted into the casing 1, the resistance element 7 including theshorter strip 11 being placed in the bottom portion 2 of the casing,while the element 8 including the longer strip 12 being placed in theupper intermediate portion 3 of the casing.

For the purpose of forcing the strips outwardly and closely against theinner sides of .the portions 2 and 3 of the casing Within which they arelocated the said casing is provided upon its inner side with awedgeshaped projection 18.which is tapered and widens from the toptoward the bottom, as is clearly shown in Fig. 4 of the drawing. Theincllnation of the opposite ends of the strips 11 and 12 is the same asthe angle of taper of the wedge 18, so that as the strips with theresistance coils thereon are pushed downwardly into place they arepushed outwardly so that their outer sides are caused to seat closelyagainst the inner sides of the adjoining portions of the casing. Themembers 7 and 8 having been Ypositioned within the casing 1 they arethen fastened to the easing by suitable fastening means such, forexample, as tubular rivets 20 which extend through openings 21 providedin the opposite ends of the strips 11 and 12 and through registeringopenings 22 provided in the adjoining portions of the wall of thecasing 1. The outer ends of the rivets, which fasten the opposite endsof the member 7 to the casing, also engage and hold the terminal stripsor bars 24, to the outer ends of which wires (not shown) are connectedwhich form parts of an external electric circuit. The rivets'by whichthe opposite ends of the member 8 are secured in place to the casing 1engage and hold terminal strips or bars 25 to which wires, not shown,are connected which also form parts of an external circuit.

For the purpose of supporting adjustable or movable contacts whichrespectively cooperate with the resistance elements or members 7 and 8 Ihave provided an opening 30 in the bottom of ,the casing 1 within whichis located a tubular bearing member 31 the inner end of which projectsinto the interior of the casing 1 to a point above or beyond the outeredge of the element or member 7 and slightly beyond the inner edge ofthe element or member 8. The tubular bearing member 31 is providedintermediate its ends with a shoulder 32 whichl is seated against theportion of the inner side of the bottom of the casing 1 whichconstitutes the inner edge of the opening 30. The outer end portion ofthe tubular b earing 31 is screw threaded for the reception of a nut 33which cooperates with the shoulder 3 2 to hold the said bearing memberin place in said opening. The nut 33 also is clamped against the base 35of a metal terminal strip or bar 36 to which a wire, not shown, isconnected which forms a part of an electric circuit, as for example, thecircuit including the filament and battery of a radio receptionapparatus. The base 35 is provided with an opening therethrough throughwhich the screw threaded portion of the tubular sleeve 31 extends. Thescrew threaded portion of the tubular sleeve 31 also extends through anopening provided in the panel 37 of a radio receiving or other apparatusand is held therein by a clamping nut 38 in known manner and asindicated in Fig. 2 of the drawing. A rotatable member or shaft 40 ismounted within the tubular bearing 31. The shaft 4() isprovided near itsouter end with a groove 41 Within which is removably mounted a ring 42for limiting the movement of the shaft 40 inwardly of the tubularbearing 31. Portions of the shaft 40 upon opposite sides of the innerend thereof are cut away as indicated to provide a flattened portion 43of general or approximately rectangular shape in cross section. Theinner ends of these cut-away portions terminate in shoulders 44. Theportion 43 extends through a correspondingly shaped opening 45 providedin the inner end of a spring metal contact 46 the outer end 47 of whichis in contact with the upper or outer edge of the resistance member 7.The contact 46 comprises spaced leg-like portions 48 which are providedwith bends 49 intermediate their ends so that the upper and lowerportions of the contact are arranged in general parallel relation toeach other as shown. The separated ends of these legs are connected by acrosswise extending portion 50 within which the opening 45, 'previouslyreferred to, is located. The presence of the bends imparts increasedyielding and resilient qualities to the contact 46. The terminal 36 haselectrical connection with the contact 46 through the tubular bearing 31and the shaft 40.

A flat member 51 of suitable insulating material also is mounted uponthe portion 43 of the shaft 40 in overlying relation to the portion 50of the contact 46. The member 51 is provided with an opening 52 ofgeneral rectangular shape which fits the correspondingly shaped portion43. The said contact and the member 51 are held in position by upsettingthe outer end of the portion 43 as indicated at 53.

For the purpose of yieldingly holding the shaft 40 inwardly with theremovable ring 42 in contact with the outer end of the tubular bearing31 I have provided a spring Washer 54 which is located between the innerend of the tubular bearing 31 and the portion 50 of the Contact. Theshaft 40 is frictionally held in any position to which it may beadjusted by rotation. Rotation of the said shaft may be effected bymeans of the knob 55 secured to the outer end thereof.

A contact 56 which engages the upper or outer edge of the resistanceelement or member 8 is supported upon the member 51 of insulatingmaterial. The contact 56 is spaced outwardly from the insulating member51 and is provided at its inner end with an off set portion 57terminating in an outwardly extending portion 58 which is secured bymeans of rivets 59 to the said insulating member 51. Both the contacts46 and 56 rotate with the shaft 40 when the latter is rotated and intheir rotation change the positions of their points of contact with theresistance elements or members 7 and 8. The contact 56 comprises spacedortions 60. An integral portion 61 extends rom the portion 58 into thespace between the portions 60, the said portion 61 being located inalinement with the shaft 40. The inner end of a stationary contact 62engages the outer side of the portion 61. The contact 62 is connected bya suitable fastening means 63, such as a tubular rivet, with anoverhanging por- -tion 64 of the casing 1. The said rivet also engagesand fastens a terminal stop or bar 65 to the under side of the saidoverhanging portion 64. The said overhanging portion is provided by thepresence of a notch at 66, the formation of which is permitted by reasonof the presence of the tapered wedge-like portion 18 previously referredto. The terminal bar 65 is adapted to be. connected to a wire, notshown, having connection with some element such as the grid of a vacuumtube so that the potential thereof may be Varied.

As heretofore described, the resistance ele., ments and the co-operatingcontact members are enclosed within a cup-shaped casing 1 having an openend for which a closure member 67 is provided. This closure member maybe made of metal and is preferably so constructed as to be readilypositioned upon the casing and removed therefrom. A marginal flange'maybe provided for the closure member, as shown in Fig. 2, for locating thesame on the casing and for removably re=I taining it thereon. Such aclosure permits ready access to the interior of the casing Wheneverthisis desirable.

It will be noted that by my invention 1 have provided a construction ofadjustable resistance means, utilizable as a potentiometer andspecifically as a volume control means for radio reception apparatus,wherein two separate and independent resistance members are mounted inconcentric relation to the same axis, the said members, however, beinglocated in different planes which extend transversely of the said axis.In other words, the said resistance members are located in differentpositions in the direction. of the axis so that they are suitably`positioned for cooperation with two separate and independent movable oradjustable contacts .which are mounted upon and are rotatably adjustableby single shaft.

It also will be seen that by my invention I have provided means wherebythe resistance members, as they are inserted into the casing of thedevice, automatically are wedged or pushed outwardly against the innerside of the wall of the said casing.

Having thus described lmy invention, what l claim and desire to secureby Letters Patent is:

1. In an adjustable resistance device, the combination of a casinghaving portions the interiors of which are of different diameters andalso having upon its inner side a wedgeshaped projection which istapered from the bottoni toward the top, relatively iiat resistancemembers located in the said casing, one of the said members beingpositioned in the portion of smaller diameter and the other in theportion of larger diameter of said casing, and the opposite ends of saidresistance members being in engagement with the opposite sides of thewedge-shaped projection, contact members for said resistance members,and an adjustable support for the said contact members.

2. ln an adjustable resistance device, the combination of asubstantially cylindrical casing having a closed end and an open end, aprojection extending inwardly from the outer wall of the casing andtapering outwardly from the open end of the casing toward the closed endthereof, a resistance element arranged within the casing with theopposite ends thereof in engagement with said projection, means forsecuring the resistance element to the casing, a Contact membercooperating with the resistance element, and n adjustable support forthe contact mem- 1n testimony that I claim the foregoing as my inventionl have hereunto signed my name this 10th day of November, 1930.

CARL L. WEICHELT.

the rotary movement of a engaging the

